Income Taxes (Schedule of Effective Income Tax Rate Reconciliation) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income taxes
Earnings before income tax	$ 235,888	$ 190,763	$ 152,512
Statutory federal and provincial tax rate in Canada	27.00%	27.00%	27.00%
Expected income tax expense	$ 63,690	$ 51,506	$ 41,178
Non-deductible expenses	4,732	3,705	4,810
Adjustments to prior years provision to statutory tax returns	(865)	4	1,323
Changes in the valuation of deferred tax assets	(2,027)	(550)	(771)
Different tax rates of subsidiaries operating in foreign jurisdictions	(12,016)	(11,818)	(17,145)
U.S. tax reform impacts	17,105	6,949	4,899
Change in enacted tax rates	391	(1,016)	93
Unrecognized tax benefits	817	(2,347)	(1,800)
Benefits of deductible stock options vested and exercised	(4,070)	(1,780)	(2,434)
Other	(2,227)	(3,030)	853
Income tax expense	$ 65,530	$ 41,623	$ 31,006